The method and the switching arrangement refer to the identification of pinching situations with electrically driven displacing drives in motor vehicles such as for example window lifts, sliding roofs or seat adjustment devices.
For displacing drives of this type there are diverse regulations and guidelines such as 74/60EWG (European Community) of the European Union, EC21 of the United Nations Economic Commission for Europe (UNECE) and FMVSS118 of the American National Highway Traffic Safety Administration. Under certain operational and testing conditions all these regulations demand a limitation of the pinching force to a maximum of 100 Newton. In 74/60/EWG and EC21 elasticity of the described testing body is indicated with 10 N/mm. In FMVSS118 for testing bodies, with a diameter of less than 25 mm, an elasticity of 65 N/mm is indicated and for larger testing bodies it is an elasticity of 20 N/mm. For safe protection of the vehicle passengers with all pinching situations occurring in practice a protection system must be able to identify pinching bodies with very different elastic forces.
For this purpose a number of protection systems is known in prior art.
From EP-A-0 716 492 it is known how to generate a difference from a last measured current value and respective values stored in a first intermediary storage. These differences are stored in a second intermediary storage. These individual differences stored in the second intermediary storage are compared with different references from a fixed value storage. If from now on one of the values from the second intermediary storage is higher than an associated value from the fixed value storage the drive is reversed or stopped.
From US-A-2003/222610 it is known how to determine with an electrically driven motor the speed reduction of the motor and how to further proceed this gained quantity.
In DE 27 27 518 for realizing a pinching protection system it is proposed to determine the clamping force via a defined distance or a defined time and to integrate and/or differentiate these determined values. If the result of these operations exceeds a value stored before, the drive is switched off or the moving direction is reversed.
In supplement DE 27 56 972 to DE 27 27 518 it is proposed to determine the rise of the force from the rise of the motor current.
In DE 30 34 118 a pinching protection system is described, which continuously determines measured values which are dependent on the rotational speed or on the speed of the aggregate or on the control device and compares them with a limiting value referring to the initial measured value and in case of exceeding the limiting value reverses for a short time the displacing direction of the control unit and then switches off the control unit.
From DE 33 03 590 a protection system is known, which determines the course of the performance of the drive motor. The drive motor is stopped or its actuation direction is reversed, if the performance-distance-diagram exceeds an associated performance-tolerance limit.
In DE 35 32 078 it is described for realizing a pinching protection system to determine the changes of the motor current during the closing motion in constant time intervals and to compare these changes to a limiting value. When exceeding the limiting value, it is switched over to the opening motion.
EP 331 659 describes a protection circuit, which determines the motor current in uniform time intervals. The motor is switched off, if the motor current exceeds by a given value an average value formed by several dating back values.
From DE 40 00 730 a method is known, in which one parameter, which refers to the displacing force and the distance covered by the displacing part is determined. Determination is performed of at least one derivation of the parameter according to the distance. The results of the derivation are compared with the limiting values and in case of exceeding the limiting value the drive is switched off or the actuation direction is reversed.
In all aforementioned methods a parameter is determined, which refers to the absolute displacing force or to the rise of the displacing force within a certain time Δt or within a certain distance Δs. If the parameter exceeds a certain threshold value g, the drive is switched off or the moving direction is reversed. In case of a pinching situation, in which the entire elasticity of the drive and of the pinching body is 20 N/mm, within 5 mm a pinching force of 100 N is formed. If the entire elasticity, however, is only 5 N/mm, after 5 mm displacing distance only a force of 25 N has been set up.
The mentioned methods all have the disadvantage that the parameters time Δt, distance Δs and threshold g cannot be adjusted such that with soft as well as with hard pinching bodies the identification of pinching situations is guaranteed and simultaneously sufficient robustness against faulty initiating is given.
In DE 40 00 730 for solving this problem it is proposed to form the derivation of the parameters on the basis of different distance sections and to compare these individual results to different limiting values. The division calculation necessary for calculating the derivation by means of the microcomputers usually used in such systems is time-consuming. In order to meet all the time requirements of the system, it may become necessary when calculating several derivations to use a more powerful and thus more costly microcomputer.
For identifying several pinching scenarios it is proposed in DE 198 40 162 A1 to perform several parallel calculations with different sets of parameters, the sets of parameters of the individual calculations being optimized for certain pinching scenarios.
With the two last mentioned methods the increased calculating expenditure for the additional calculations and the increased storage requirement for the individual sets of parameters is disadvantageous. A further disadvantage is that such a method can be optimized only for a limited number of pinching scenarios.
From DE 199 41 475 a two-step method for adaptation to different spring rates is known, in which the change of the rotational speed is determined and added up. In the first step the added-up change in rotational speed is compared with a threshold and when exceeding this threshold the second step of the method is started. In the second step then the added-up change in rotational speed is compared with a predetermined chronological limiting value course and when exceeding this limiting value the drive is switched off or reversed. Also this method comprises the disadvantage that the threshold in the first step and the predetermined tolerance Δ in the second step can only be optimally adjusted for one spring rate.
DE 198 40 164 A1 describes a method for adjusting a movable vehicle part between at least two positions, the vehicle part being driven by an electric motor. Here, a pulse signal is produced proportionally to the rotational movement of the electric motor and is supplied to a control unit for controlling the motor, the time of the input of each signal being determined at the control unit, and at certain times a value for the change of the motor rotational speed being determined from at least one part of these times measured so far. From each changing value of the rotational speed a changing value of the force is calculated and at least one part of the changing values of the force determined so far is added-up with a weighting, in order to determine a value for the current force influence onto the movable vehicle part, this value being used as a criteria in the decision whether the motor is switched off or reversed or not. In this connection a force-dependent and threshold-value-based weighting of the changing values of the force is performed such that the weight of a changing value of the force is zero, as far as the value lies below the lower threshold value, whereas the weight for all succeeding values, which exceed this threshold value, is one. In this method the weighting serves for a threshold-value-based selection of individual changing values of the force for the adding-up.
It is the object of the invention to indicate a method, which makes it possible in simple manner to realize a pinching protection system for drive systems in motor vehicles, by means of which soft as well as hard pinching bodies can be detected and with which simultaneously a high reliability is given with regard to faulty initiating.